Upon discovery, oil is first produced, from reservoirs, where possible, by the natural gas pressure therein. When the pressure becomes too low, the oil is then extracted with the assistance of mechanical lifting means or pumps of varying design and manner of operation. This production is referred to as primary production. When primary recovery becomes too slow, too low or totally ceases, the reservoirs usually contain well over 50% of the original oil and frequently contain over 75% and as high as about 90% to 95% of the original oil. Accordingly, it has long been the practice to use one or more secondary means of increasing the recovery of the crude oil. Among the more successful, economical and widely used secondary processes are water displacements or water floods, wherein water is pumped down one or more injection wells and out through a reservoir towards one or more production wells, pushing the oil ahead of the water-drive. Even after a successful water flood, however, about half the original oil remains in the reservoir. Much of its exists as individual globules of "residual" oil which are immobile.
Several tertiary recovery processes have been proposed to recover substantial amounts of the oil remaining in a reservoir after water flooding. Among these is injection of an aqueous solution of one or more surfactants. If properly chosen, the surfactants drastically reduce the interfacial tension between fluid phases in the reservoir and allow the residual oil globules to move. They ultimately coalesce into a continuous oil phase which flows to the production wells.
One group of effective surfactants are the carboxylic acid soaps or saponified acids which includes the natural soaps of crude oil acids. A process using such petroleum acid soaps has additional advantages over other surfactants in that they can be readily formed in-situ by injection of caustic into the reservoirs to be treated. However, an important disadvantage of such soaps are the relatively low and varying amounts of petroleum acids of the crude in different pores and/or parts of a reservoir. This provides for unpredictable and inefficient results. Additionally the caustic which is injected is frequently adsorbed or otherwise reacts with the formation so that it is thereby lost for purposes of saponification and utilizable soap or surfactant.
Other surfactants used are commercial ones such as petroleum sulfonates because of their relatively low cost and their potential availability in large quantities. However, these surfactants are effective in displacing oil only when salinities are relatively low, i.e. less than about 10% by weight. Preflushes to obviate the salinity problem have met with limited success.
Nonionic surfactants have been considered because they are not limited to low salinity but on the other hand they are quire expensive.
Another synthetic surfactant which is relatively inexpensive and potentially available in large quantities is saponified tall oil pitch. Tall oil pitch is the bottoms, a waste product from pulp paper manufacture by the sulfate process. This surfactant alone is relatively effective but nevertheless leaves room for improvement.
Strong incentives exist, therefore, to develop an improved surfactant flooding process for acidic crudes using the cheaper surfactant compositions.